Many recent studies have demonstrated that carcinogens act as mutagens in microbial test systems and cultured mammalian cells. It is unclear, however, whether the mutagenic action of carcinogenesis is related to their oncogenic potential or is an unrelated phenomenon. Since carcinogens have a wide variety of other effects on living cells including alterations in DNA, RNA and protein synthesis, membrane changes, changes in gene expression and toxic effects, it would be of interest to begin to evaluate the role of these events and mutagenesis in the oncogenic process. We have begun to examine mutagenesis and in vitro transformation simultaneously in the same cell lines and to evaluate the dosimetry of these processes using isotopically labeled carcinogens. The objective is to help clarify what role, is any, mutagenesis plays in transformation and carcinogenesis.